Running in America’s worst air: ‘Like binging on a carton of cigarettes’

For a writer and runner in Denver, Colorado, the city's severe air pollution creates a daily dilemma: do something you love, or risk your health?

Outdoor runners have always had a lot of data to juggle: their pace, heart-rate, mileage, route, calories, weather and much more. Though in recent years there's been a new, considerably more ominous data point for alfresco athletes to monitor: the Air Quality Index (AQI).

The index, which measures the level of air pollution at any given time and location, is an increasingly necessary tool for outdoor enthusiasts in the age of climate change.